1. Field of the Invention
The present invention relates to radio frequency (RF) communications and, more particularly, to a method and apparatus for providing a dual-loop phase lock loop in a radio-frequency (RF) receiver.
2. Description of the Related Art
Increasing market penetration of wireless communications or simply, wireless devices, such as cellular telephones, radios, global navigation satellite systems (GNSS) receivers/transceivers, and the like, is generally premised on reducing costs associated with deployment of such devices while maintaining or improving performance and/or adding features thereto. One way to accomplish this task is to continually improve upon the devices' components that perform electronic functions for wireless communications. For example, through continuous improvement of such components, newer generations of such wireless devices are routinely deployed in smaller packages with more processing power and lower power consumption, yet cost less than their earlier counterparts.
One way to lower cost and improve performance is to use digital circuitry in substantially all of the subcomponents of a receiver. Digital circuits can be formed on a single substrate (i.e., monolithically) or a small number of substrates within an integrated circuit package that allow for improved power consumption as well as processing power. Such receivers are capable of receiving signals at very low signal strengths as well as providing digital signal processing in a single receiver integrated circuit.
Although most components within a digital receiver are digital in nature, certain components operate in the analog domain and are mounted “off chip”. Such components include, for example, a low-noise amplifier, which functions to amplify RF signals; a mixer circuit, which functions to down-convert the RF signals; resistors and capacitors used by phase lock loop (PLL) circuits; and an automatic gain control (AGC) circuit, which functions to control a dynamic range of the receiver. To improve performance of the receiver, utilizing digital circuitry for as many components of a receiver as possible is desirable.
In particular, a conventional PLL circuit may use capacitor-based integrator and/or operational amplifiers that do not facilitate a single or multiple integrated circuit solution because capacitors and resistors used by the capacitor-based integrator and/or the operational amplifiers are located externally from the integrated circuit in which the PLL circuit is formed.
Furthermore, conventional PLLs utilize two-stage search and lock strategies that are time and power consuming. These two-stage search and lock strategies often require that the conventional PLLs undergo recalibration when tuning voltages run out of range. Such recalibration occurs the conventional PLLs are powered on for a prolonged time period, which may cause changes in temperature and/or other conditions that effect calibration. The re-calibration can be very problematic for RF receivers because the time and power spent on recalibration cannot be used for processing incoming signals.
Therefore, there is a need in the art for a method and apparatus for providing a fully integrated (i.e., no external components), dual-loop PLL within an RF receiver.